1. Field of the Invention
This invention relates to a filter assembly for a luminaire, which assembly provides the sole passageway for air passage between the sealed enclosure and the exterior of the luminaire. More particularly, the present invention relates to providing a cap for the filter assembly that protects the filter from the elements and permits the filter assembly to be located in an exposed portion of the luminaire.
2. Description of the Prior Art
In high intensity discharge (HID) luminaires, such as those used for street lighting and industrial lighting in atmospheres containing impurities and contaminants, a sealed optical enclosure is desired. This sealing maintains the lighting power of the luminaire by keeping contaminants out of the system. For outdoor units, the sealing of the optical enclosure is particularly important to prevent rain and other elements and contaminants from entering the enclosure to avoid damage to and shorting of the electrical components of the luminaire.
Since sealed HID luminaires operate at relatively high temperatures, a pressure relief mechanism or breather is provided to let hot air escape during operation and to let air enter when the luminaire is turned off and permitted to cool. This pressure relief is necessary to alleviate the thermal stress which adversely affects the life of the lamp, the other electrical components in the luminaire and the glass lens.
Conventional pressure relief devices, such as that disclosed in U.S. Pat. No. 3,457,399 to Milroy, comprise a vent filled with a charcoal filter. The charcoal filter is air permeable, permitting hot air to escape from the sealed enclosure of the luminaire when the lamp is hot and cool air to enter into the sealed enclosure when the lamp cools. Since the filter is the sole air passageway to or from the sealed enclosure, the filter prevents impurities or contaminants from entering and building up in the sealed enclosure. By preventing contaminants from entering the sealed enclosure, such adverse effects on the luminating level of the optical system as dulling films, and corrosion and discoloring of the reflecting surface and glass lens are avoided.
In the outdoor luminaire embodiment disclosed in the Milroy patent, the filter assembly is located in a lower rear portion of the luminaire adjacent the ballast. The filter housing is a resilient tubular holder which is open at its opposite ends. The filter assembly is positioned within the luminaire housing adjacent the ballast to protect the filter assembly from the elements. In the industrial embodiment disclosed in the Milroy patent for indoor use, the filter assembly is located in an aperture in the reflector with its exterior surface exposed.
Conventional filter assemblies, such as that disclosed in the Milroy patent, are disadvantageous in that they can not be provided in the optimum location in the luminaire for the most efficient operation thereof and still be protected from the environment. For optimum effectiveness of the filter assembly, it should be located directly in the optical section at the upper part of the luminaire. However, for outdoor lighting, the filter assemblies have been located adjacent the ballast compartment at the bottom of the housing to prevent rainwater from getting into the housing through the charcoal filter assembly. Locating the filter assembly at the ballast compartment limits the aiming and placement of the luminaire with respect to mounting brackets or cross arms to the top mounting mode only.